In one aspect, the invention relates to a method for operating a combined heat and power supply system. According to another aspect, the invention relates to an apparatus for supplying heat and power.
In a gas turbine process, compressed air is fed to a combustion chamber in which combustion of a fuel takes place. The combustion produces high pressure and temperature exhaust gas. This high pressure and temperature gas drives the turbine blades which turn a shaft. The mechanical power of the shaft is used to drive a load; typically an electrical generator.
Most gas turbine processes require waste heat recovery on the turbine exhaust to achieve an acceptable overall efficiency. This is called a combined cycle. Usually, the turbine exhaust gas is directed through a steam boiler to produce low-pressure steam or hot water that is used for operation of space heating equipment, domestic hot water heaters, and absorption refrigeration equipment.
A problem arises in utilizing a combined cycle because the waste heat boiler duty will be dependent on the shaft power load even though the steam demand may be totally unrelated to the shaft power load demand. Thus at times an excess of useful exhaust heat will exist, and at other times a deficiency will exist.
In the past a deficiency in useful exhaust heat has been overcome by burning additional fuel in the exhaust stream or by providing a supplemental furnace. The later is not thermally efficient, and the former is expensive and complex to install. On the other hand, an excess of exhaust heat results in wasted energy, lower thermal efficiency and lowered profitability.